Multi-lumen catheters and, in particular split-tip catheters, are desirable for various treatment applications such as hemodialysis where fluid extraction and infusion occur simultaneously. Hemodialysis is the separation of metabolic waste products and water from the blood by diffusion through a semipermeable membrane. Typically, a hemodialysis unit is connected to a patient's body by a catheter. The catheter's distal end is placed in a blood vessel and its proximal end is connected to a hemodialysis unit.
During hemodialysis, a patient's blood flows through a double lumen catheter to the hemodialysis unit which provides filtration and controls the flow of blood. A double lumen catheter has two lumens that independently allow fluid extraction and return. For example, one lumen can be used for removing blood from a patient for processing in the hemodialysis machine and the other lumen can be used for subsequently returning the processed blood back to the patient's circulatory system.
Parameters that can be varied to achieve adequate hemodialysis include blood flow rate, dialysis solution flow rate, dialyzer competency, and temperature. Generally, raising the blood flow rate increases dialyzer clearance of small molecular weight solutes. Consequently, higher blood flow rates have been used to improve dialysis clearance efficiency. However, conditions such as access recirculation decrease clearance. Access recirculation is the recirculation of treated blood back into the hemodialysis unit causing inadequate dialysis. This problem effectively reduces blood flow rates thereby diminishing the efficiency of the hemodialysis process causing the duration of the treatment needed for dialysis to increase. Access recirculation can be particularly of concern when using a double lumen catheter due to the close proximity of the intake and outflow ports at the distal tip of the catheter.
Various double lumen catheter designs have been suggested for the purpose of reducing access recirculation. The distal ends of intake and outflow lumens have been longitudinally spaced 20-30 mm apart to prevent recirculation. For example, Twardowski et al. U.S. Pat. No. 5,569,182 discloses that the lumen for return of blood back into the vein should terminate beyond the extraction lumen. The purpose of this is to prevent cleansed blood, exiting from the outlet point of the catheter, from re-entering the catheter's blood inlet point and returning to the dialysis machine. However, certain disadvantages have been noted by such large longitudinal spacing between the distal ends of the respective lumens. For example, blood flow stagnation in the region of the blood vessel between two widely separated tips can lead to clot formation.
In addition to longitudinal spacing of the distal openings of the lumens for blood extraction and return, others have suggested that the distal end of a multi-lumen catheter can be split such that the distal tips of the lumens can independently move in the blood vessel to optimize the fluid dynamics of the different functions (blood extraction and blood return).
In general, good catheter outcomes depend on proper positioning of the catheter in the blood vessel. Insertion complications include pneumothorax, hemothorax, and cardiac tamponade, as well as poor blood flow rates, poor clearances, and long-term complications such as catheter dysfunction and fibrin sheath formation. These complications are compounded by the use of double lumen catheters because of their size.
Additional difficulties can be encountered when split distal tips must be inserted into a blood vessel. Typical insertion techniques of conventional double lumen catheters require the use of a peel-away sheath over a guidewire. Frequently there is a preference to insert the catheters without the use of a peel-away sheath to eliminate the risk of an air embolism by the use of two guidewires, or alternatively, inserting the guidewire through the one lumen and threading it through the side hole channels of the other lumen thus utilizing one guidewire, referred to as the “weave technique”. Moreover, precise positioning of a multi-lumen catheter can be challenging because the exact placement of the tips can not be assured. An improperly positioned multi-lumen catheter can further result in sub-optimal functionality requiring intervention.
Thus, there remains a need for a multi-lumen catheter that addresses the problems of access recirculation yet retains the comparative ease of insertion of a single lumen catheter.